Currently, many computer-controlled systems must be available on substantially a full-time basis. Transaction processing systems, for example, sometimes must be accessible at any time of the day or night in order to permit ongoing activities. Telephone switching, and the supporting data processing transaction services, for example, must be available at all times. The supporting transaction processing system that permits "800 Calling" service and credit card calling is one such service. In the process of dialing 800 calls, for example, the telephone system must access a data base containing the appropriate translation of the 800 number into a standard telephone number for controlling the switching path. This is accomplished by routing the call to a special switching office called a Service Switching Point (SSP). The SSP switch launches a message requesting the necessary translation to an appropriate Switching Control Point (SCP) processor over a Common Channel Signaling (CCS) network made up of a plurality of redundant Signalling Transfer Points (STPs). The STPs, using addressing information in the header of the packet, ensure that the launched message packet is routed to the SCP having the required translation. The SCP, in turn, looks up the required information, encapsules it in a message packet and launches the message on the CCS back to the requesting SSP. The SSP then uses this information to select an appropriate inter-exchange carrier, if necessary, to deliver the telephone number to the carrier for completion of the call, or to complete the call in the local area.
In systems such as that described above, the software in the SCP must be of extremely high reliability and must be available essentially continuously. A serious problem therefore arises when it is necessary to update or change the software in an SCP. Removing the SCP from service for this purpose is not always possible, particularly if no suitable substitute is available. The present invention is directed at systems and methods for replacing or updating system software without removing the corresponding computer from service.
Every software application package is made up of a plurality of programmed processes designed to work together to produce the desired results. The operating system itself is likewise made up of a plurality of different processes working together. In order to ensure that the various programmed processes in a computer installation work together harmoniously, the interfaces between such processes are carefully crafted so that data passing between the processes is properly formated by the sending process so as to be properly received by the receiving process. If the inter-process protocols are not changed by the updating of one or more processes, then each process can be changed in situ, without regard for the other processes. One such a process replacement technique is disclosed in the copending application of B. A. Redman, Ser. No. 238,485, filed Aug. 31, 1988, now Pat. No. 4,954,941 and assigned to applicants' assignee.
On the other hand, when the software updating involves a plurality of processes and involves changes in the inter-process protocols, it is then necessary to ensure that all of the processes are changed simultaneously, or at least as a group, since none of the old processes will operate properly with any of the new processes. This problem is particularly difficult in real time data processing systems such as the telephone transaction processing system described above, where the software cannot be taken out of service for any significant length of time. It is toward software systems of this type that the present invention is directed.
In some systems of this type, it has become necessary to provide an entire second spare system to back up the main system. The new software is then installed on the back-up system, tested, and put on line by switching between systems. One such system is described in "Life Cycle Support and Update of No. 4 ESS Software," by E. A. Davis and R. J Healey, 1982 IEEE Document No. 0536-1486/82/0000-0216, page 5G5.1, 1982. It is extremely expensive, however, to provide and entire duplicate system, particularly simply to permit software retrofitting. More often, a single system, whether using one processor or many, must be updated without the luxury of a physical duplicate being available. It is toward this kind of environment that the present invention is directed.